Method for managing the propulsive power of an aircraft

ABSTRACT

A method for managing the propulsive power of an aircraft, the aircraft extending longitudinally along an axis X from the rear forwards and comprising at least two lateral propulsion systems each comprising a fan, each lateral propulsion system having a fan rotation speed N 2  and at least one rear propulsion system configured to ingest a boundary layer of said aircraft, the rear propulsion system comprising a fan having a fan rotation speed N 3 , the management system comprising, during a cruising phase P 4 , a step of adjusting the rotation speed N 3  of the rear propulsion system according to the following formula N 3 =a*N 2  in which a is a constant.

TECHNICAL FIELD

The present invention relates to an aircraft comprising at least onelateral propulsion system and at least one rear propulsion system whichis mounted at a rear point of the aircraft in order to ingest a boundarylayer of the aircraft. The invention relates, more particularly, to amethod for managing propulsion systems during the different phases ofdisplacement of the aircraft.

In a known manner, an aircraft extends longitudinally along an axis andcomprises lateral wings on which are mounted lateral propulsion systems,in particular, turbine engines. In order to increase the propulsionefficiency of an aircraft, it is known to mount a rear propulsion systemat a rear point of the aircraft in order to ingest an air flow of theboundary layer of the aircraft. As a reminder, the boundary layer isformed at the surface of the fuselage. In a boundary layer, the maximumvelocity of the air flow is equal to 99% of the free velocity.Consequently, the air flow of the boundary layer is displaced moreslowly than the free air flow. Thus, when a rear propulsion system isconfigured to ingest the air flow of the boundary layer, the rearpropulsion system generates an air flow with a lower exhaust velocitythan the lateral propulsion systems placed under the wings of theaircraft and configured to absorb the flow of free air, which increasesthe efficiency of the rear propulsion system.

At present, the rear propulsion system is used at constant power in thedifferent displacement phases (take off, idle on the ground and inflight, climb and cruise, etc.) in order to reduce the power of thelateral propulsion systems and thus limit the consumption of theaircraft.

In practice, the power supplied by the rear propulsion system may leadto disruptions of the lateral propulsion systems, which can lead toproblems of operability as well as surge problems of the lateralpropulsion systems. In actual fact, the greater the contribution of therear propulsion system, the more important the aforementioned drawbacks.

The management of the power of a rear propulsion system is particularlycomplex given that it has to be, on the one hand, maximized to enable areduction in the fuel consumption of the aircraft and, on the otherhand, limited to reduce the risk of disruptions of the lateralpropulsion systems.

The aim of the invention is to overcome these drawbacks by proposing anovel method for managing in an optimal manner the power of a rearpropulsion system.

In an incidental manner, an entirely electrical architecture withoutthermal lateral systems is known from the patent applicationUS2018/118356A1.

SUMMARY

To this end, the invention relates to a method for managing thepropulsive power of an aircraft, the aircraft extending longitudinallyalong an axis X from the rear forwards and comprising at least twolateral propulsion systems each comprising a fan, each lateralpropulsion system having a fan rotation speed N₂ and at least one rearpropulsion system configured to ingest a boundary layer of saidaircraft, the rear propulsion system comprising a fan having a fanrotation speed N₃.

The invention is remarkable in that it comprises, during a cruise phaseP4, a step of adjusting the rotation speed N₃ of the rear propulsionsystem 3 according to the following formula:

N ₃ =a*N ₂

in which a is a constant.

In an advantageous manner, during a cruise phase, the speed of the rearpropulsion system N₃ is synchronized with the speed N₂ of the fans ofthe lateral propulsion systems, in such a way as to optimize theperformances of the rear propulsion system and lateral propulsionsystems. In a preferred manner, the fan of a lateral propulsion systemhaving a diameter d2, the fan of a rear propulsion system having adiameter d3, the method comprises, during a cruise phase P4, a step ofadjusting the rotation speed N₃ of the rear propulsion system accordingto the following formula:

d ₃ *N ₃ =b*d ₂ *N ₂

in which b is a constant comprised between 0.85 and 1.15.

In an advantageous manner, the head speeds of the fan blades are equal.A constant b comprised between 0.85 and 1.15 makes it possible to offera power variation of 15% which is acceptable for conserving optimalperformances. Preferably, the lateral propulsion systems are thermal insuch a way as to produce thrust and electrical power. In a preferredmanner, the lateral propulsion systems are in the form of turbineengines.

Further preferably, the method comprises during a climb phase P1 of theaircraft, a step of adjusting the rotation speed N₃ of the rearpropulsion system to a first reference rotation speed N_(S1) in such away as to supply a first predetermined constant propulsive power VP₁.

In an advantageous manner, the propulsive power of the rear propulsionsystem is restrained to a power value VP₁ used during the climb phaseP1. This is particularly advantageous to improve the lifetime of therear propulsion system, in particular, when it comprises an electricmotor, and the lifetime of the lateral propulsion systems, inparticular, when they comprise current generators.

Preferably, the method comprises, during an idle phase P3, a step ofadjusting the rotation speed N₃ of the rear propulsion system as afunction of the rotation speed N₂ of the lateral propulsion systemswherein:

-   -   if the rotation speed N₂ of the lateral propulsion systems        multiplied by the constant a is less than the first reference        rotation speed N_(S1), the rotation speed N₃ of the rear        propulsion system is adjusted in such a way as to be a function        of the rotation speed N₂ of the lateral propulsion systems 2. In        a preferred manner, the rotation speed N₃ of the rear propulsion        system 3 is defined according to the formula N₃=a*N₂ described        previously,    -   if the rotation speed N₂ of the lateral propulsion systems        multiplied by the constant a is greater than the first reference        rotation speed N_(S1), the rotation speed N₃ of the rear        propulsion system is equal to the first reference rotation speed        N_(S1).

In an advantageous manner, during an idle phase, the speed of the rearpropulsion system N₃ is synchronized with the speed N₂ of the fans ofthe lateral propulsion systems, in such a way as to optimize theperformances of the rear propulsion system and the lateral propulsionsystems. In a preferred manner, the method comprises, during a take-offphase P2, a step of adjusting the rotation speed N₃ of the rearpropulsion system to a second reference rotation speed N_(S2) in such away as to supply a second predetermined propulsive power VP₂ strictlygreater than the first predetermined propulsive power VP₁.

During the take-off phase, it is important to supply an importantpropulsive thrust. In an advantageous manner, the rear propulsion systemis used at high speed in order to limit the fuel consumption of thelateral propulsion systems during the take-off phase and in order tolimit problems of surges of the lateral propulsion systems.

In a preferred manner, the second predetermined propulsive power VP₂ isdefined according to the following formula:

V _(p2) =V _(p1) +F1

-   -   in which F1 is a positive adaptation function which notably        depends on the altitude and the speed of the aircraft.

Thus, the rear propulsive power is increased compared to the value VP₁as a function of the flight conditions of the aircraft, in order toprevent any surge phenomenon in the lateral propulsion systems. Furtherpreferably, the positive adaptation function is also a function of theposition of the control lever and the ambient temperature.

According to an aspect of the invention, the rear propulsion systemcomprises at least one fan driven by an electric motor. An electricallysupplied rear propulsion system makes it possible to limit fuelconsumption. Preferably, the electric motor is supplied by at least onegenerator taking mechanical torque from a shaft, notably low pressure,of one of the lateral propulsion systems.

In a preferred manner, the first propulsive power VP₁ is predeterminedas a function of the continuous maximum power of the electric motor ofthe rear propulsion system. In an advantageous manner, the firstpropulsive power VP₁ is determined to maximize the ingestion of theboundary layer of the fuselage and to optimize fuel consumption.

According to an aspect of the invention, the management methodcomprises, in the event of breakdown of one of the lateral propulsionsystems, a step of adjusting the rotation speed N₃ of the rearpropulsion system in such a way as to be equal to a third referencerotation speed N_(S3) in order to supply half of the first predeterminedpropulsive power V_(P1).

Given that only one of the lateral propulsion systems is operational,the propulsive power of the rear propulsion system is decreased by 50%in order not to cause the surcharge of the only lateral propulsionsystem which is operational.

Preferably, outside of the cruise phase, the rotation speed N₃ of therear propulsion system is determined as follows N₃≤a*N₂ in such a way asto obtain optimal performances. This makes it possible to adapt therotation speed of the rear propulsion system as a function of thespecific constraints linked to the climb, the idle and the take off.

Preferably, each lateral propulsion system comprising at least one bleedvalve, the method comprises, in the event of breakdown of the rearpropulsion system, a step of opening the bleed valves of the lateralpropulsion systems. The absence of rear propulsion causes a strongcompression in the low pressure compressors of the lateral propulsionsystems. The opening of the bleed valves makes it possible to limit thepressure and thus to avoid a surge phenomenon of the low pressurecompressors of the lateral propulsion systems.

The invention also relates to a computer program comprising instructionsfor the execution of the steps of a management method such as describedpreviously when said program is executed by a computer.

The invention further relates to an electronic unit for aircraftcomprising a memory comprising instructions of a computer program suchas described previously. Finally, the invention also relates to anelectronic unit such as described previously.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood on reading the description thatfollows, given uniquely as an example, and by referring to the appendeddrawings in which:

FIG. 1 is a schematic representation of an aircraft with a rearpropulsion system according to the invention,

FIG. 2 is a schematic representation of propulsion systems and anelectronic unit,

FIG. 3 represents a functional block diagram of the climb phase of themanagement method according to the invention,

FIG. 4 represents a functional block diagram of the take-off phase ofthe management method according to the invention,

FIGS. 5 and 6 represent a functional block diagram of the idle phase ofthe management method according to the invention,

FIG. 7 represents the variation in the rotation speed of the rearpropulsion system as a function of the rotation speed of the lateralpropulsion system during the idle phase for constant flight conditions,

FIG. 8 is a representation of a functional block diagram of the cruisephase of the management method according to the invention,

FIG. 9 is a representation of a functional block diagram of themanagement method according to the invention in the event of breakdownof a lateral propulsion system, and

FIG. 10 is a representation of a functional block diagram of themanagement method according to the invention in the event of breakdownof a rear propulsion system.

It should be noted that the figures set out the invention in a detailedmanner for implementing the invention, said figures obviously being ableto serve to better define the invention if need be.

DETAILED DESCRIPTION

With reference to FIG. 1, an aircraft 1 is represented extendinglongitudinally along an axis X and comprising lateral wings on which aremounted lateral propulsion systems 2, in particular, thermal systemssuch as turbine engines. Such a thermal lateral propulsion system 2makes it possible to generate thrust. In a preferred manner, the lateralpropulsion system is a dual flow turbine engine. It comprises in apreferred manner a low pressure compressor, a high pressure compressor,a low pressure turbine and a high pressure turbine.

In order to increase the propulsion efficiency of an aircraft, theaircraft 1 further comprises a rear point 11 on which is mounted a rearpropulsion system 3 in order to ingest an air flow of the boundary layerof the aircraft 1. As a reminder, the boundary layer is formed at thesurface of the fuselage. In a boundary layer, the maximum velocity ofthe air flow is equal to 99% of the free velocity. Consequently, the airflow of the boundary layer is displaced more slowly than the free airflow. Thus, when a rear propulsion system 3 is configured to ingest theair flow of the boundary layer, the rear propulsion system 3 generatesan air flow with a lower escape velocity than the lateral propulsionsystems 2 placed under the wings of the aircraft and configured toabsorb the free air flow, which increases the efficiency of the rearpropulsion system 3. Subsequently, each lateral propulsion system 2 hasa rotation speed N₂. In this example, each lateral propulsion system 2comprises a fan and the rotation speed N₂ corresponds to the fan speedN₂. In a preferred manner, the fan is rotationally integral with the lowpressure compressor.

The rotation speeds N₂ of the two lateral propulsion systems 2 areequal. As will be described hereafter, each lateral propulsion system 2comprises at least one bleed valve configured to discharge the airsituated in a compression stage of a lateral propulsion system 2. In ananalogous manner, the rear propulsion system 3 has a rotation speed N₃.In this example, the rear propulsion system 3 comprises a fan and therotation speed N₃ corresponds to the fan speed N₃. In this example, theaircraft 1 further comprises an electronic unit 4 connected to thelateral propulsion systems 2 and to the rear propulsion system 3 inorder to control their respective speeds N₂, N₃. The electronic unit 4is in the form of an electronic card receiving different information andmeasurements of the aircraft 10 and the propulsion systems 2, 3.

In this exemplary embodiment, with reference to FIG. 2, the rearpropulsion system 3 comprises a fan 30 which is driven by an electricmotor 31 which is itself controlled by the electronic unit 4. A rearpropulsion system 3 makes it possible to supply thrust while limitingfuel consumption, which is advantageous. In a preferred manner, theelectric motor 31 is supplied by one or more electrical generators 20which take mechanical power from the lateral propulsion systems 2. For alateral propulsion system 2 being in the form of a double-bodyturbomachine comprising a low pressure shaft and a high pressure shaft,mechanical power is preferably taken from the low pressure shaft.

An exemplary embodiment of a method for managing the propulsive power ofan aircraft 1 according to different phases of displacement of theaircraft 1 will henceforth be described. In this example, the managementmethod is implemented by the electronic unit 4.

In particular, as is described hereafter, the management method aims toadjust the propulsive power P₃ of the rear propulsion system 3 byadjusting the rotation speed N₃ of the rear propulsion system 3according to the displacement phase of the aircraft 1 and as a functionof the rotation speed N₂ of the lateral propulsion systems 2.

The electronic unit 4 measures in real time the value of the rotationspeeds N₂, N₃ of the lateral propulsion systems 2, 3. Moreover, theelectronic unit 4 determines the displacement phase of the aircraft 1 asa function of different parameters of the aircraft 1, in particular, thealtitude, the position of the throttle lever controlling the lateralpropulsion systems 2, the speed of the aircraft and the ambienttemperature, etc. Thus, the electronic unit 4 makes it possible todetect the transition from one displacement phase to another. In anadvantageous manner, the electronic unit 4 can modify the value of therotation speed N₃ of the rear propulsion system 3 in an optimal manneras a function of the displacement phase of the aircraft 1. In thisexemplary embodiment, the electronic unit 4 comprises a memory 40 inwhich are stored parameters.

A management of the propulsive power will henceforth be describedaccording to the following displacement phases: a climb phase P1, atake-off phase P2, an idle phase P3 and a cruise phase P4.

In this exemplary embodiment, the rotation speed N₃ of the rearpropulsion system 3 is determined as a function of the rotation speed N₂of the two lateral propulsion systems 2.

With reference to FIG. 3, during a climb phase P1, the electronic unit 4adjusts the rotation speed N₃ of the rear propulsion system 3 in such away that it is equal to a first reference rotation speed N_(S1) in sucha way as to supply a first predetermined propulsive power VP₁. The firstreference rotation speed N_(S1) is predetermined and stored in a memoryof the electronic unit 4. Preferably, the first reference rotation speedN_(S1) is a function of the altitude, the flight speed and the ambienttemperature. In practice, for a first predetermined propulsive powerVP₁, the first reference rotation speed N_(S1) varies as a function ofthe flight conditions.

Thus, during the climb phase P1, the first predetermined propulsivepower V_(P1) does not depend on the rotation speed N₂ of the lateralpropulsion system 2. In a preferred manner, the first propulsive powerVP₁ is determined in such a way as to correspond to the maximumcontinuous power of the electric motor 30 of the rear propulsion system3. This advantageously makes it possible to use the rear propulsionsystem 3 in order to ingest a maximum of boundary layer and to minimizefuel consumption.

With reference to FIG. 4, during a take-off phase P2, the electronicunit 4 adjusts the rotation speed N₃ of the rear propulsion system 3 insuch a way as to be equal to a second reference rotation speed N_(S2) insuch a way as to supply a second predetermined propulsive power VP₂. Thesecond reference rotation speed N_(S2) is predetermined and stored inthe memory 40 of the electronic unit 4. In a preferred manner, thesecond reference rotation speed N_(S2) is a function of the altitude,the flight speed and the ambient temperature. For the same flightconditions, the second reference rotation speed N_(S2) is strictlygreater than the first reference rotation speed N_(S1) in such a waythat the second predetermined propulsive power V_(P2) is strictlygreater than the first predetermined propulsive power V_(P1). Inpractice, the second reference rotation speed N_(S2) varies as afunction of the flight conditions.

Indeed, in the take-off phase P2, the aircraft 1 requires an importantpropulsive power. The important use of the rear propulsion system 3makes it possible to limit the fuel consumption of the lateralpropulsion systems 2 and to prevent any surge phenomenon in the lateralpropulsion systems 2.

In a preferred manner, the second propulsive power V_(P2) is determinedaccording to the following formula: V_(p2)=V_(p1)+F1 in which F1 is apositive adaptation function that depends on the altitude of theaircraft, the speed the aircraft, the position of the control lever andthe ambient temperature. In this example, the adaptation function F1 isstored in the memory 40 of the electronic unit 4.

During the take-off phase P2, the rear propulsion system 3 is highlyloaded for a short period. Finally, with reference to FIG. 8, during acruise phase P4, the electronic unit 4 adjusts the rotation speed N₃ ofthe rear propulsion system 3 according to the following formula:

N ₃ =a*N ₂

in which a is a constant.

In a preferred manner, the fan of a lateral propulsion system 2 having adiameter d2 and the fan of a rear propulsion system 3 having a diameterd3, the method comprises a step of adjusting the rotation speed N₃ ofthe rear propulsion system 3 according to the following formula:

d ₃ *N ₃ =b*d ₂ *N ₂

in which b is a constant comprised between 0.85 and 1.15.

Thus, according to the invention, the head speeds of the fan blades aresubstantially equal. This enables optimal dimensioning of the propulsionsystems.

In an advantageous manner, during the cruise phase P4, the rearpropulsion system 3 is used in such a way as to optimize both itsefficiency and the performances of the lateral propulsion systems 2. Therotation speed N₃ is synchronized with the rotation speed N₂ in order tooptimize the performances.

With reference to FIG. 5, during an idle phase P3, the electronic unit 4adjusts the rotation speed N₃ of the rear propulsion system 3 as afunction of the rotation speed N₂ of the lateral propulsion system 2.Idle phase P3 is taken to mean not just an idle phase on the ground butalso an idle phase in flight.

As an example, FIG. 7 is a schematic representation of an idle phaseduring which the flight conditions do not change. With reference toFIGS. 5 and 7, if the rotation speed N₂ of the lateral propulsionsystems 2 multiplied by the constant a is less than the first referencerotation speed N_(S1) (a*N₂<N_(S1)), the rotation speed N₃ of the rearpropulsion system 3 is adjusted in such a way as to be a function of therotation speed N₂ of the lateral propulsion systems 2. In a preferredmanner, the rotation speed N₃ of the rear propulsion system 3 is definedaccording to the formula N₃=a*N₂ described previously.

Thus, the rear propulsion system 3 delivers a propulsive power less thanthe first predetermined propulsive power V_(P1) and adapts to the powerof the lateral propulsion systems 2 to obtain optimal performances.

Conversely, with reference to FIGS. 6 and 7, if the rotation speed N₂ ofthe lateral propulsion systems 2 multiplied by the constant a is greaterthan the first reference rotation speed N_(S1) (a*N₂>N_(S1)), then therotation speed N₃ of the rear propulsion system 3 is equal to the firstreference rotation speed N_(S1). Thus, the rear propulsion system 3delivers a propulsive power that is limited to the first predeterminedpropulsive power V_(P1). According to the management method, therotation speed N₃ of the rear propulsion system 3 is restrained in sucha way as to avoid the operating limits of the rear propulsion system 3being exceeded. Moreover, this makes it possible to avoid the rearpropulsion system 3 from operating outside of its high-efficiency range,which is advantageous.

With reference to FIG. 7 representing a theoretical case with constantflight conditions, over the period t0-t1, when the speed N₂ of thelateral propulsion systems 2 multiplied by the constant a is less thanthe first reference rotation speed N_(S1) (a*N₂<N_(S1)), the rotationspeed N₃ of the rear propulsion system 3 is adjusted in such a way as tobe a function of the rotation speed N₂ of the lateral propulsion systems2. In a preferred manner, the rotation speed N₃ of the rear propulsionsystem 3 is defined according to the formula N₃=a*N₂ describedpreviously. Over the period t1-t2, when the rotation speed N₂ of thelateral propulsion systems 2 multiplied by the constant a is greaterthan the first reference rotation speed N_(S1) (a*N₂>N_(S1)), therotation speed N₃ of the rear propulsion system 3 is equal to the firstreference rotation speed N_(S1).

In FIG. 7, the first reference rotation speed N_(S1) is constant but itgoes without saying that it could be variable as a function of theflight conditions.

With reference to FIG. 9, the management method also makes it possibleto treat critical cases of breakdown of one of the lateral propulsionsystems 2. Indeed, during a breakdown of one of the lateral propulsionsystems 2, the electronic unit 4 adjusts the rotation speed N₃ of therear propulsion system 3 in such a way as to be equal to a thirdreference rotation speed N_(S3) in order to supply half of the firstpredetermined propulsive power V_(P1). In this example, the thirdreference rotation speed N_(S3) is notably a function of the altitude,the flight speed and the ambient temperature.

In practice, the electronic unit 4 measures a dysfunction DYS2 of one ofthe lateral propulsion systems 2 and transmits a rotation speedinstruction N_(S3) to the rear propulsion system 3 as illustrated inFIG. 9 in order to supply half of the first predetermined propulsivepower V_(P1). In other words, the rear propulsion system 3 decreases itsinfluence in order to avoid supplying a greater propulsive power thanthat which the lateral propulsion system 2 which is in operation iscapable of supplying. Given that 50% of the lateral propulsive power isprevented on account of the breakdown of one of the lateral propulsionsystems 2, the rear propulsive power 3 may be decreased in aproportional manner in order to guarantee optimal operation.

With reference to FIG. 10, said management method also makes it possibleto treat the critical case of breakdown of the rear propulsion system 3.In the present case, during a breakdown of the rear propulsion system 3,the electronic unit 4 imposes the opening of the bleed valves of thelateral propulsion systems 2 in order to avoid the appearance of a surgephenomenon. The bleed valves, known by the person skilled in the art as“variable bleed valves” advantageously make it possible to avoid airoverpressures inside the compressor of a turbomachine of a lateralpropulsion system 2 while outwardly venting a quantity of air liable tocause a surge. In practice, the electronic unit 4 measures a dysfunctionDYS3 and transmits an instruction to open the bleed valves VBV of thelateral propulsion systems 2 as illustrated in FIG. 10.

Thanks to the invention, the different propulsion systems 2, 3 aremanaged in an optimal manner for any displacement phase.

Outside of the cruise phase P4, the rotation speed N₃ of the rearpropulsion system 3 is determined as follows N₃≤a*N₂ in such a way as toobtain optimal performances, in particular, vis-à-vis the firstpredetermined propulsive power VP₁ for the climb P1 and the idle P3 andvis-à-vis the second predetermined propulsive power V_(P2) for thetake-off phase P2.

1-11. (canceled)
 12. A method for managing the propulsive power of anaircraft, the aircraft extending longitudinally along an axis X from therear forwards and comprising at least two thermal lateral propulsionsystems each comprising a fan, each lateral propulsion system having afan rotation speed N2 and at least one rear propulsion system configuredto ingest a boundary layer of said aircraft, the rear propulsion systemcomprising a fan having a fan rotation speed N₃, management methodwherein, during a cruise phase P4, a step of adjusting the rotationspeed N₃ of the rear propulsion system according to the followingformula:N ₃ =a*N ₂ in which a is a constant.
 13. The management method accordingto claim 12, wherein, the fan of a lateral propulsion system having adiameter d2, the fan of a rear propulsion system having a diameter d3,the method comprises, during a cruise phase P4, a step of adjusting therotation speed N₃ of the rear propulsion system according to thefollowing formula:d ₃ *N ₃ =b*d ₂ *N ₂ in which b is a constant comprised between 0.85 and1.15.
 14. The management method according to claim 12, comprising,during a climb phase P1 of the aircraft, a step of adjusting therotation speed N₃ of the rear propulsion system to a first referencerotation speed N_(S1) in such a way as to supply a first predeterminedconstant propulsive power VP₁.
 15. The management method according toclaim 14, comprising, during an idle phase P3, a step of adjusting therotation speed N₃ of the rear propulsion system as a function of therotation speed N₂ of the lateral propulsion systems wherein: if therotation speed N₂ of the lateral propulsion systems multiplied by theconstant a is less than the first reference rotation speed N_(S1), therotation speed N₃ of the rear propulsion system is adjusted according tothe following formula:N ₃ =a*N ₂ if the rotation speed N₂ of the lateral propulsion systemsmultiplied by the constant a is greater than the first referencerotation speed N_(S1), the rotation speed N₃ of the rear propulsionsystem is equal to the first reference rotation speed N_(S1).
 16. Themanagement method according to claim 14, comprising during a take-offphase P2, a step of adjusting the rotation speed N₃ of the rearpropulsion system to a second reference rotation speed N_(S2) in such away as to supply a second predetermined propulsive power VP₂ strictlygreater than the first predetermined propulsive power VP₁.
 17. Themanagement method according to claim 16, wherein the secondpredetermined propulsive power VP₂ is defined according to the followingformula:V _(p2) =V _(p1) +F1 in which F1 is a positive adaptation function whichdepends notably on the altitude and the speed of the aircraft.
 18. Themanagement method according to claim 14, wherein the rear propulsionsystem comprising at least one fan driven by an electric motor, thefirst propulsive power is predetermined as a function of the continuousmaximum power of the electric motor of the rear propulsion system. 19.The management method according to claim 14, comprising: in the event ofbreakdown of one of the lateral propulsion systems, a step of adjustingthe rotation speed N₃ of the rear propulsion system in such a way as tobe equal to a third reference rotation speed N_(S3) in order to supplyhalf of the first predetermined propulsive power V_(P1).
 20. Themanagement method according to claim 12, wherein each lateral propulsionsystem comprising at least one bleed valve, the method comprising: inthe event of breakdown of the rear propulsion system, a step of openingthe bleed valves of the lateral propulsion systems.
 21. The managementmethod according to claim 12, wherein outside of the cruise phase, therotation speed N₃ of the rear propulsion system is defined according tothe following formula N₃≤a*N₂.
 22. A computer program comprisinginstructions for the execution of the steps of the management methodaccording to claim 12 when said program is executed by the computer.